Shearing mechanism

ABSTRACT

A spring actuated reciprocable shearing member having a spring biased actuator for resetting the shearing member in a retracted position and a latch for holding the shearing member in the retracted position. In the cutting operation, the actuator is first withdrawn against the bias of its spring and then the shearing member is actuated by its spring upon release of the latch.

O Un1ted States Patent 1 111 3,731,576 Smilgys et al. May 8, 1973 541 SHEARING MECHANISM [56 References Cited Robert C. Ritchie, Feeding Hills, Mass 686,967 11/1901 2,642,936 6/1953 [7 3] Assignee: Veeder Industries Inc., Hartford, 3,068,732 12/1962 Conn. 3,257,886 6/1966 3,474,696 10 1969 [22] Filed: June 2, 1972 I 211 App] 259 234 Primary ExaminerFrank T. Yost Attorney-Prutzman, Hayes, Kalb & Chilton Related US. Application Data [63] Continuation of Ser. No. 80,260, Oct. 13, 1970, Pat. [57] ABSTRACT A spring actuated reciprocable shearing member having a spring biased actuator for resetting the shearing 83/616 member in a retracted position and a latch for holding [51] Int. Cl. ..B 26d 5/08 the shearing member in the retracted position, In the [58] Field of Search ..'85/587, 590, 616, cutting operation, the actuator is first withdrawn 85/586,588 against the bias of its spring and then the shearing member is actuated by its spring upon release of the latch.

7 Claims, 7 Drawing Figures PAIENIEUHAY 81m 3.731.578

SHEET 1 [IF 3 PATENTEDW 81975 3,731,576

SHEET 3 BF 3 FIG. 3 /z SHEARING MECHANISM This application is a continuing application of applicants copending application Ser. No. 80,260 filed Oct. 13, 1970, now US. Pat. No. 3,668,375, and entitled Printer.

BRIEF SUMMARY OF THE INVENTION The present invention relates generally to shearing mechanisms and more particularly to a new and improved shearing mechanism having notable utility in a fuel dispensing apparatus printer for severing a printed record of each fuel delivery from a paper strip.

It is a primary aim of the present invention to provide a new and improved shearing mechanism for fuel dispensing apparatus operable at the completion of each fuel delivery for severing a printed record of the fuel delivery from a paper strip.

It is a further aim of the present invention to provide a new and improved shearing mechanism operable for shearing paper.

Other objects will be in part obvious and in part pointed out more in detail hereinafter.

A better understanding of the invention will be obtained from the following detailed description and the accompanying drawings of an illustrative application of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a generally schematic representation, partly broken away, of a gasoline delivery pump employing a printer incorporating the present invention;

FIG. 2 is an enlarged front elevation view, partly broken away and partly in section, of the printer;

FIG. 3 is an enlarged side elevation view, partly broken away and partly in section of the printer;

FIG. 4 is a partial section view, partly broken away and partly in section, taken substantially along line 4- 4 of FIG. 2 and showing a ratchet mechanism of the printer;

FIGS. 5 and 6 are partial section views, partly in section, taken substantially along line 55 of FIG. 2 and showing acam mechanism of the printer in normal and intermediate operating positions thereof; and

FIG. 7 is a partial section view, partly in section, showing a lost motion coupling of the printer.

' DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings in detail wherein like numerals represent like parts, a gasoline delivery pump 10 employing a printer l2 incorporating the present invention is shown comprising a delivery register 14 (for example of the type disclosed in U. S. Pat. No. 3,216,659 of Edward C. Ambler et al. dated Nov. 9, 1965 and entitled Resetting Control Mechanism for Counting Device") having volume and cost counters I5, 16 for registering the volume and cost for each fuel delivery and a reset shaft 17 adapted to be rotated one revolution for resetting the volume and cost counters l5, 16 to 0."

An electrical drive unit 18 (for example of the type disclosed in U. S. Pat. No. 3,662,866 of Silvio Conte dated May 16, I972 and entitled Drive Unit for Fluid Delivery Pump) is mounted on the left side of the register 14 for rotating the reset shaft 17 one revolution for resetting the register prior to the commencement of each fuel delivery. The electrical drive unit 18 is also connected via an intermediate shaft 20 and a coupling 22 to rotate a printer operating shaft 24 one revolution after the completion of each fuel delivery for sequentially printing a ticket or receipt 26 and resetting the printer for the succeeding fuel delivery. In a conventional manner the gasoline delivery pump 10 incorporates a fuel pump 32 driven by an electric motor 34 for delivering gasoline from a suitable source (not shown) through a fluid meter 35 to a dispensing nozzle 36. The output or volume shaft 40 of the meter 35 is connected for driving the volume counter 15 for registering the volume of fuel delivered and for driving a variator 42 (for example of the type disclosed and described in U. S. Pat. No. 3,413,867 of Richard B. Hamlin dated Dec. 3, 1968 and entitled Variator"). The variator 42 is connected for driving the cost counter 16 for registering the cost of the fuel delivered in accordance with the volume of fuel delivered and a unit volume price established by the variator setting. As described more fully in said U. S. Pat. No. 3,662,866 of Silvio Conte, the electric drive unit 18 is operable by a handle 52 such that when the handle is rotated (e.g., in the counterclockwise direction)to its horizontal or On position, the electric drive unit 18 is operated to rotate the reset shaft 17 one revolution for sequentially resetting the register 14 and conditioning the pump 10 for delivering gasoline. When the operating handle 52 is rotated in the opposite direction to its Off or vertical position shown in FIG. 1, the electrical drive unit 18 is operated for sequentially de-energizing the pump motor 34 and rotating the printer operating shaft 24 one revolution.

The printer 12 comprises a frame with a pair of side plates 66, 68 and a number of rotary shafts extending between the side plates. A cost printing counter 80 is provided for printing the cost of each fuel delivery and if desired a similar volume printing counter may be provided for printing the volume of each fuel delivery. The cost counter 80 has five counter wheels 82-86 of increasing order rotatably mounted on a shaft 88 and the lowest order counter wheel 82 is connected (via gears 90, 91, a uni-directional spring drive clutch 92, and a coupling 94) to be rotated (in the clockwise direction as viewed in FIG. 3) by the variator 42 in conjunction with the rotation of the lowest order counter wheel of the cost counter 16. A U-shaped bail or yoke 96 is pivotally mounted on the counter shaft 88 and a transfer pinion shaft 100 is supported on the bail. Conventional mutilated transfer pinions 102 are mounted on the pinion shaft 100 for engagement with the counter wheels 82-86 for generating transfers between adjacent lower and higher order wheels in a conventional manner.

Each counter wheel 82-86 comprises a molded 0" .9" type or print wheel 103, a combined locking ring and transfer gear segment 104 integrally molded with the print wheel 103 and a separate 20-tooth molded drive gear 106 (and for example are constructed as shown and described in U. S. Pat. No. 2,382,708 of Sterling Graydon, Jr. et al. dated Aug. 14, I945 and entitled Resettable Counter). The print wheels 103 may be rotated in the adding direction (clockwise as viewed in FIG. 3) relative to the respective drive gears 106 (for resetting the print wheels 103 to while the transfer pinions 102 remain in engagement with the wheel drive gears 106 and combined locking ring and transfer gear segments 104), and the counter shaft 88 has an axial slot 108 for receiving pivotal reset pawls 109 mounted on the print wheels 103 for resetting the type wheels in the adding direction to O.

A serial printing counter 110 having three coaxial counter wheels 1 12-114 rotatably mounted on counter shaft 88 (and having an integral construction but otherwise like the counter wheels 82-86) is provided for printing successive serial numbers on successive tickets 26. Conventional mutilated transfer pinions 120 rotatably mounted on pinion shaft 100 are provided for indexing the wheels 113, 114 in a conventional manner and a similar mutilated pinion 122 also rotatably mounted on shaft 100 engages the -tooth drive gear 124 of the lowest order counter wheel 112 for rotating the counter wheel 112 relative to the other counter wheels 113, 114 as hereinafter described.

A date printer module 130 is mounted on the printer operating shaft 24 for printing the date on each ticket 26. The date printer module 130 comprises a support hub or sleeve 132 having ten equiangularly spaced (i.e., spaced 36) axial detent grooves 133 and three pairs of O9 print wheels 134 having individual ball detents 136 engageable with the detent grooves 133 of the support sleeve 132. The print wheels 134 may be individually angularly set on the support sleeve 132 for printing the date with the month, day and year each designated by a pair of numerals in a conventional manner. An end washer 140 is affixed onto the inner end of the support sleeve 132 and has a depending tang 142 receivable within an axial slot 144 in the support shaft 24 for keying the date printer module 130 to the shaft. A collar 146 is rotatably mounted on the outer end of the sleeve 132 and is supported within a bushing 148 in the side plate 68. The collar 146 provides a knob for axially withdrawing the date printer module 130 to a withdrawn position shown in part in broken lines in FIG. 2 (where the tang 142 engages a stop pin 152) to provide access for manually setting the date print wheels 134. Thus, the date printer may be easily set at the beginning of each day by merely withdrawing the date printer module 130 and manually setting the print wheels 134 as necessary. A diametrically extending detent spring 156 is mounted on the end of the collar 146 and the shaft 24 is provided with a detent annulus 158 for receiving the detent spring 156 for holding the date printer module 130 in its inner or operative position shown in full lines in FIG. 2.

The printer operating shaft 24 is rotated in the clockwise direction as viewed in FIG. 3 and the counter shaft 88 is connected by gears 160-162 to be rotated by shaft 24 in the adding direction, clockwise as viewed in FIG. 3. Shafts 163, 164 for backup or ink rolls 165, 166 respectively are connected to the operating shaft gear 160 by suitable gearing 400, 401, 402 (shown in broken lines in FIG. 3) to be rotated by shaft 24, in the counterclockwise direction as viewed in FIG. 3, and a pair of cam shafts 168, 169 are also connected by the gearing 401, 402 and a gear 403 mounted on the cam shaft 168 to be rotated, by the operating shaft 24, in the clockwise direction as viewed in FIG. 3. As hereinafter described, the gear 403 is connected to drive the cam shaft 168 through a lost motion coupling 410 interconnecting the gear 403 and the cam shaft 168. The shafts 24, 88, 163, 168, 169 are connected by 1:1 gearing to be rotated through one revolution together for operating the printer.

A suitable paper roll (not shown) is provided, and as seen in FIG. 3 the paper strip 180 is fed downwardly from the roll between the coaxial cost and serial counters 80, and corresponding backup roll and between the date printer 130 and corresponding backup roll 166. The backup rolls 165, 166 are made porous and impregnated with a suitable ink and have raised portions 182 such that when the shaft 24 is rotated one revolution the raised type on the date printer module 130 at station 184 and the raised type on the cost and serial counters 80, 110 at station 185 cooperate with the raised portions 182 on the rolls 165, 166 to provide a printout on the paper 180.

Referring to FIGS. 5 and 6 a cam mechanism 200 operated by counter shaft 88 is provided for oscillating the transfer pinion shaft 100 during the rotation of the counter shaft 88. The cam mechanism 200 provides for pivoting the transfer pinion shaft in the adding direction approximately 54 from its normal or withdrawn position shown in full lines in FIGS. 2-5 (during the first 48 of rotation of counter shaft 88) for sequentially (a) readying the cost and serial counters 80, 110 for printing and (b) rotating the cost and serial counters 80, 110 as a unit with the counter shaft 88 to produce a printout. Upon rotation of the counter shaft 88 through a succeeding 312 to complete a revolution, the cam mechanism 200 pivots the pinion shaft 100 54 back to its initial or normal operating position while counter wheels 82-86 are reset to 0 by counter shaft 88.

During the 54 return movement of the pinion shaft 100, a one-way locking pawl 202 (FIG. 3) engages the 20-tooth drive gear 124 to hold the lowest order serial counter wheel 112 against return movement and to thereby index the counter wheel 112 54 or 1% counts (i.e., one-half count excess) in the adding direction relative to the remaining counter wheels 113,1 14. The drive pinion 122 which engages the lowest order wheel drive gear 124 rotates on the transfer pinion shaft 100 as the pinion shaft 100 returns to its normal or retracted position and a pivotal spring biased locking cam 204 which engages the alternate long teeth 206 of the drive pinion 122 is pivoted outwardly by the long" teeth 206 as the drive pinion 122 rotates on the pinion shaft 100. With the pinion shaft 100 in its normal or fully withdrawn position, a long" tooth 206 of the drive pinion 122 is substantially perpendicular to locking cam 204 and upon the succeeding operation of the printer (and forward pivotal movement of the pinion shaft 100) the drive pinion 122 is rotated by the locking cam 204 approximately 45 (until two long teeth 206 engage the locking cam 204 to lock the drive pinion 122 against further rotation) to in effect index thelowest order counterwheel one-half count in the subtracting direction relative to the remaining serial counter wheels 1 13, 114 to offset the prior one-half excess count.

Referring to FIG. 4, a lO-tooth ratchet wheel 240 is keyed to the drive gear 106 of the lowest order cost wheel 82 and a ratchet pawl mechanism 242 is mounted on the pinion shaft 100 for engagement with the ratchet wheel 240. The ratchet pawl mechanism comprises a support lever 244 rotatably mounted on pinion shaft 100 and biased by a spring 246 in the counterclockwise direction as viewed in FIG. 4 and a pawl 248 pivotally mounted on support lever 244. With the pinion shaft 100 in its normal operating position shown in FIG. 4, a tail 250 of support lever 244 engages a shaft 252 to pivotthe lever 244 clockwise as viewed in FIG. 4 about the pinion shaft 100 to permit a leaf spring 256 to withdraw the pawl 248 substantially out of engagement with the ratchet wheel 240. During approximately the first of forward pivotal movement of the pinion shaft 100 the support lever 244 is pivoted by spring 246 to pivot pawl 248 into engagement with the ratchet wheel 240 and if the wheel 82 were at an intermediate count position for example at the one-half count or beyond, to engage a ratchet tooth and index the counter wheel 82 to the next higher full count position. If the wheel 82 were at a lower intermediate count position the pawl 248 will engage the ratchet wheel 240 to rotate the wheel 82 with the remaining cost counter wheels 83-86 (as the pinion shaft 100 is pivoted forwardly) in which case the wheel 82 is in effect indexed to its next lower full count position.

The cam mechanism 200 comprises a cam plate 210 pivotally mounted on shaft 212 and having a slot for receiving the transfer pinion shaft 100. The cam plate 210 has a central opening contoured to provide an inner cam edge 214 engageable by a roller' 216 mounted on a collar 218 fixed onto the counter shaft 88. The collar 218 provides an outer cam edge 220 and a stud or follower 222 is mounted on the cam plate 210 for engagement with the outer cam edge 220. The inner and outer cam edges 214, 2 20 cooperate to pivot the pinion shaft 100 forwardly approximately 54, in the clockwise direction as viewed in FIGS. 5 and 6, from its normalor fully withdrawn angular position shown in FIG. 5 during the initial 48 of rotation of the shaft 88, and then backwardly 54 to its normal operating position during the remaining 312 of rotation of shaft 88.

After the counter shaft 88 is rotated approximately 4 from its normal operating position shown in FIG. 5 the cam follower 222 is released by the cam edge 220 to permit the pinion shaft 100 to be pivoted by spring 246 forwardly approximately 10 to its position shown in FIG. 6 for operating the ratchet pawl mechanism 242. During the succeeding approximately 44 of rotation of counter shaft 88 the roller 216 engages the inner cam edge 214 to pivot pinion shaft 100 with the counter shaft 88 (and therefore rotate the cost and serial counters 80, 110 as a unit with the counter shaft 88) during which unitary motion the type wheels of the cost and serial counters 80, 110 cooperate with the backup roll 165 to print the cost of the fuel delivery and the ticket serial number. During the remaining 312 of rotation the outer cam edge 220 engages the follower 222 to return the pinion shaft 100 to its fully withdrawn or normal position, and the counter shaft 88 resets the cost counter print wheels to 0" During the last 356 of rotation of the counter shaft 88 (i.e., after the follower 222 has been released to permit the pinion shaft to rotate approximately 10) the shaft 88 rotates approximately 366 (i.e., 6 more than a full revolution) relative to the pinion shaft 100 and therefore 366 relative to the counter print wheels thereby ensuring that the print wheels are fully reset to 0" with only 360 of rotation of the counter shaft 88.

Referring to FIGS. 2 and 3 a shear mechanism 280 is provided for severing the printed ticket 26 from the paper strip. The shear mechanism 280 comprises a first fixed plate 282 and a second shear plate or guillotine 284 reciprocably mounted for cooperation with the fixed plate 282 for shearing the ticket from the paper strip. The shear plate 284 has an intermediate inclined shearing edge 288, and a pair of laterally spaced tension springs 290 are connected to the lateral ends of the shear plate for actuating the shear plate 284 in one direction for shearing the paper. A latch lever 291 and a drive or actuating lever 292 are pivotally mounted on the cam shafts 168, 169 respectively and have lower ends received within slots in the shear plate 284 for controlling the motion of the shear plate. A tension spring 296 is provided for pivoting the drive lever 292 in the counterclockwise direction as viewed in FIG. 3 for actuating the shear plate 284 to a retracted position shown in part by broken lines in FIG. 3 for which purpose the tension spring 296 is sufficiently strong to overcome the bias of the drive springs 290.

A control cam 300 is mounted on cam shaft 168 for pivotally withdrawing the pivotal drive lever 292, holding the drive lever 292 in its withdrawn position and timely releasing the drive lever for withdrawing the shear plate 284. The control cam 300 operates (as hereinafter described) to release the lever 292 immediately after the paper has been sheared and so that the shear plate 284 is in its withdrawn position (shown in part in broken lines in FIG. 3) between fuel deliveries and during a subsequent fuel delivery and until the printer is operated again to provide a record of the succeeding delivery. Such facilitates feeding the paper also permits feeding the succeeding ticket downwardly between the plates 282, 284 for being sheared by the shearing mechanism.

The latch lever 291 provides for holding the shear plate 284 in its fully retracted position after the shear plate 284 has been retracted by the drive lever 292 and a control cam 304 mounted on shaft 169 provides for maintaining the shear plate 284 latched in its retracted position by the latch lever 291 until just prior to the completion of the full revolution of the printer operating shaft 24 at which point the latch lever 291 and shear plate 284 are released to permit the shear plate 284 to shear ticket 26 from the paper strip.

Referring to FIG. 7 the lost motion coupling 410 is formed by a diametral drive pin 412 on the cam shaft 168 and an enlarged diametral slot 414 in the hub 416 of the drive gear 403. A coupling spring 418 is connected between the drive pin 412 and drive gear 403 to bias the shaft in the driving direction, in the clockwise direction as viewed in FIG. 3. The spring force of the coupling spring 418 is less than the resistance against rotation of the shaft 168 due to the engagement of the drive lever 292 with the control cam 300 such that the drive gear hub 416 rotates to engage the drive pin 412 to positively rotate the cam 300.

After the shear plate 284 shears the paper ticket the tail end of the drive lever 292 is engaged by the shear I plate 284 and is momentarily pivoted due to the combined bias of the drive springs 290 and momentum of the shear plate 284 to pivot the drive lever 292 off the cam 300. The cam 300 is thereby released to be rotated by the coupling spring 418 through the available lost motion of for example 10 provided by the lost motion coupling 410 to release the drive lever 292 for retracting the shear plate 284. Accordingly, the shear plate 284 is first released by the latch lever 291 to shear the ticket from the paper strip, and at the completion of the shearing operation of the drive lever 292 is momentarily withdrawn to release the control cam 300 and thereby release the drive lever 292 to immediately return the shear plate 284 to its retracted position.

Referring to FIGS. 1 and 2, the drive coupling 22 between intermediate shaft and printer operating shaft 24 is designed to permit rotation of the printer operating shaft 24 in the correct angular direction only and to ensure proper angular alignment of the shafts 20, 24. For this purpose the drive coupling member 320 has a pair of diametrically related drive pins or teeth 322 at different radial distances from the axis of the shaft 22 and the gear 160 which functions as the driven coupling member has a pair of diametrically related pockets 328 at the same radial distances from the axis of the shaft 24 for receiving drive pins 322. Also, the pin receptacles 328 and the drive pins 322 are tapered to provide for rotating the shaft 24 in one angular direction only, in the clockwise direction as viewed in FIG. 3.

As will be apparent to persons skilled in the art, various modifications, adaptations and variations of the foregoing specific disclosure can be made without departing from the teachings of the present invention.

We claim:

1. In a shearing mechanism having a reciprocable shearing member operable in opposite directions between extended and withdrawn positions for performing a shearing operation and an operating mechanism for operating the shearing member in its opposite directions, the improvement wherein the operating mechanism comprises first spring means biasing the shearing member in one direction to one position thereof, a reciprocable actuator operable in one direction thereof for actuating the shearing member in its opposite direction to its other position, second spring means biasing the actuator in its said one direction to actuate the shearing member in its said opposite direction to its said other position against the bias of said first spring means, a releasable latch for releasably latching the shearing member in its said other position, and control means for sequentially withdrawing the actuator against the bias of the second spring means, releasing the latch to permit the shearing member to be actuated in its said one direction by the first spring means, and releasing the actuator to be actuated by the second spring means to actuate the shearing member in its said opposite direction.

2. A shearing mechanism according to claim 1 wherein the actuator and latch are pivotally mounted and the control means comprises rotary cam means for sequentially pivotally withdrawing the actuator against the bias of the second spring means, releasing the pivotal latch to permit the shearing member to be actuated in its said one direction by the first spring means, and releasing the actuator to be pivotally actuated by the second spring means to actuate the shearing member in its said opposite direction.

3. A shearing mechanism according to claim 2 wherein the rotary cam means provides for pivoting the latch to a latching position thereof for latching the shearing member in its said other position.

4. A shearing mechanism according to claim 1 wherein the shearing member is operable by said first spring means in said one direction to perform said shearing operation.

5. A shearing mechanism according to claim 1 wherein the control means is operated by the shearing member to automatically release the actuator as the shearing member is moved to its said one position by the first spring means.

6. A shearing mechanism according to claim 1 wherein the control means comprises a rotary cam adapted to be rotated in one angular direction thereof for withdrawing the actuator against the bias of the second spring means and then releasing the actuator, a rotary input, a lost motion coupling interconnecting the rotary input and rotary cam, coupling spring means interconnecting the rotary input and rotary cam biasing the cam in its said one angular direction, the actuator being engageable with the cam to angularly withdraw the cam relatively to the rotary input against the bias of the coupling spring means as the cam is rotated in its said one angular direction by the rotary input, the shearing member being operable to engage the actuator as the shearing member moves in its said one 

1. In a shearing mechanism having a reciprocable shearing member operable in opposite directions between extended and withdrawn positions for performing a shearing operation and an operating mechanism for operating the shearing member in its opposite directions, the improvement wherein the operating mechanism comprises first spring means biasing the shearing member in one direction to one pOsition thereof, a reciprocable actuator operable in one direction thereof for actuating the shearing member in its opposite direction to its other position, second spring means biasing the actuator in its said one direction to actuate the shearing member in its said opposite direction to its said other position against the bias of said first spring means, a releasable latch for releasably latching the shearing member in its said other position, and control means for sequentially withdrawing the actuator against the bias of the second spring means, releasing the latch to permit the shearing member to be actuated in its said one direction by the first spring means, and releasing the actuator to be actuated by the second spring means to actuate the shearing member in its said opposite direction.
 2. A shearing mechanism according to claim 1 wherein the actuator and latch are pivotally mounted and the control means comprises rotary cam means for sequentially pivotally withdrawing the actuator against the bias of the second spring means, releasing the pivotal latch to permit the shearing member to be actuated in its said one direction by the first spring means, and releasing the actuator to be pivotally actuated by the second spring means to actuate the shearing member in its said opposite direction.
 3. A shearing mechanism according to claim 2 wherein the rotary cam means provides for pivoting the latch to a latching position thereof for latching the shearing member in its said other position.
 4. A shearing mechanism according to claim 1 wherein the shearing member is operable by said first spring means in said one direction to perform said shearing operation.
 5. A shearing mechanism according to claim 1 wherein the control means is operated by the shearing member to automatically release the actuator as the shearing member is moved to its said one position by the first spring means.
 6. A shearing mechanism according to claim 1 wherein the control means comprises a rotary cam adapted to be rotated in one angular direction thereof for withdrawing the actuator against the bias of the second spring means and then releasing the actuator, a rotary input, a lost motion coupling interconnecting the rotary input and rotary cam, coupling spring means interconnecting the rotary input and rotary cam biasing the cam in its said one angular direction, the actuator being engageable with the cam to angularly withdraw the cam relatively to the rotary input against the bias of the coupling spring means as the cam is rotated in its said one angular direction by the rotary input, the shearing member being operable to engage the actuator as the shearing member moves in its said one direction to momentarily withdraw the actuator from the cam and thereby permit the cam to be rotated by the coupling spring means to position the cam for releasing the actuator.
 7. A shearing mechanism according to claim 1 wherein the control means comprises holding means for releasably holding the actuator in a withdrawn position thereof and wherein the shearing member is operable to release the holding means as the shearing member moves in its said one direction. 